QAbstractItemModel: fix persistent index corruption when moving columns

QHeaderView creates persistent indexes in
_q_sectionsAboutToBeChanged(), called by the slot connected to
rowsAboutToBeMoved/columnsAboutToBeMoved.

In the case of rows, QAbstractItemModel emits the signal *before*
preparing to update persistent indexes in itemsAboutToBeMoved(),
so it can see the ones newly created by QHeaderView, all is well.

In the case of columns, the emit was done *after* calling
itemsAboutToBeMoved(), so the additional persistent indexes created by
QHeaderView were ignored, and in endMoveRows() we could end up with:
ASSERT failure in QPersistentModelIndex::~QPersistentModelIndex: "persistent model indexes corrupted"

This bug has been there since the very beginning of beginMoveColumns(),
but was undetected because moving columns in a model is pretty rare
(in my case there's a QTransposeProxyModel that turns columns into
rows in the underlying model, and a proxy that handles dropMimeData...)

Change-Id: I74bad137594019a04c2a19c2abb351ff3065c25a
Reviewed-by: Andreas Buhr <andreas.buhr@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
(cherry picked from commit 74a4d88e9a002ec30b4bb7bbaf7776b458ae15db)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp b/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp
index d81c10573e..4e857c7626 100644
--- a/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp
+++ b/tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp
@@ -250,6 +250,7 @@ private slots:
     void testResetCachedSizeHint();
     void statusTips();
     void testRemovingColumnsViaLayoutChanged();
+    void testModelMovingColumns();
 
 protected:
     void setupTestData(bool use_reset_model = false);
@@ -351,6 +352,12 @@ public:
         endRemoveColumns();
     }
 
+    void moveColumn(int from, int to)
+    {
+        beginMoveColumns(QModelIndex(), from, from, QModelIndex(), to);
+        endMoveColumns();
+    }
+
     void cleanup()
     {
         emit layoutAboutToBeChanged();
@@ -3676,5 +3683,18 @@ void tst_QHeaderView::testRemovingColumnsViaLayoutChanged()
     // The main point of this test is that the section-size restoring code didn't go out of bounds.
 }
 
+void tst_QHeaderView::testModelMovingColumns()
+{
+    QtTestModel model(10, 10);
+    QHeaderView hv(Qt::Horizontal);
+    hv.setModel(&model);
+    hv.resizeSections(QHeaderView::ResizeToContents);
+    hv.show();
+
+    QPersistentModelIndex index3 = model.index(0, 3);
+    model.moveColumn(3, 1);
+    QCOMPARE(index3.column(), 1);
+}
+
 QTEST_MAIN(tst_QHeaderView)
 #include "tst_qheaderview.moc"